Steam generators are known, and in particular steam generators used in fast neutron nuclear reactors which include heat exchange tubes in which the supply water of the steam generator is heated and then vaporized after passing inside the tubes in which it flows.
The tubes of the steam generator are connected at one of their ends to a tube plate constituting one of the walls of a water box by means of which the supply water is distributed to the inside of the tubes of the bundle of the steam generator.
The tubes of the bundle are connected at their other ends to a tube plate constituting a wall of a steam manifold in which the water vapor formed in the tubes is collected.
A heat-exchange fluid, such as liquid sodium, is made to circulate in contact with the external surface of the tubes, so as to be cooled upon contact with the tubes of the steam generator and to perform the heating and vaporization of the supply water.
In particular, steam generators with straight tubes are known, such as the steam generator described in French Patent Application No. 91-14249 filed on Nov. 19, 1991, which includes straight tubes connected rigidly to the tube plates at each of their ends, the jacket of the steam generator including deformable parts made up of elements such as bellows making it possible to absorb the differential expansions between the bundle of the steam generator and the jacket.
Steam generators including rectilinear tubes are also known which are associated with expansion loops.
In fast neutron nuclear reactors, use is also made of steam generators having tubes wound into a helix which depart individually through the jacket of the steam generator by means of sleeves.
Steam generators are also known in which the U-shaped exchange tubes have two straight branches and a curved part.
In all cases, it is necessary to provide a homogeneous distribution of the supply water in the tubes of the bundle of the steam generator, level with the water box.
In the case of steam generators including tubes in a helix configuration, it has been proposed to place flow rate-restricting members inside the outer tubes connected to the tubes of the steam generator passing through the jacket by means of sleeves..
The dismantling and replacement of these flow rate-restricting members is a long and delicate operation, and it is very difficult to adapt the characteristics of the flow rate-restricting orifice plates so as to adjust the-flow rate in each of the tubes of the bundle of the steam generator to obtain stabilize the operation of the steam generator, regardless of the operating speed.
Flow rate-restricting members installed in the inlet part of the tubes of the steam generator in effect make it possible to obtain good static and dynamic stability for the operation of the steam generator. The flow rates passing through each of the tubes are balanced.
In the case of a steam generator in which it has been necessary to plug a certain number of tubes of the bundle after an incident or accident (for example, an accident having given rise to a reaction between the sodium and the water), it is proposed to place, in each of the tubes, orifice plates of adapted characteristics, so as to rebalance the flow-rates in the tubes remaining in service.
To date, no method was known for varying and to adjusting the flow rate inside a tube of a steam generator connected to a tube plate delimiting a water box in order to adapt the head loss and the flow rate of the fluid circulating in the tube, taking account of the position of the plug tubes in the bundle.